The present invention relates to a process for the production of phenolic-rich pyrolysis oils suitable for use in making phenol-formaldehyde resol resins. More particularly, the invention is directed to the production of phenolic-rich pyrolysis oils from lignocellulosic materials.
Phenol-formaldehyde or phenolic resins are typically cross-linkable polymeric resins. There are two types of phenolic resins; both types are made from phenol and aldehydes, usually pure phenol and formaldehyde. One type of phenolic resin, novolak, is made under acidic conditions using excess phenol; the acid catalyzes the reaction of phenol and formaldehyde to form the cross-linkable polymeric resin. Novolak resins are used for the formation of molded pieces and articles. The other type of phenolic resin, resol, is made under basic conditions using excess formaldehyde; a small amount of a base is added to the phenol to catalyze the reaction thereof with formaldehyde and form the cross-linkable polymeric resin. Resol resins are used as adhesives for gluing together the veneer plies of exterior-grade plywood panels and the flakes of oriented strand board panels. The cured adhesive is resistant to moisture, preventing delamination of the panels.
Because phenol is produced primarily from petroleum, its price and availability are linked to that of petroleum. Consequently, phenolic resins are relatively expensive. A number of attempts have thus been made in recent years to at least partially substitute the petroleum-based phenol in phenolic resins with inexpensive phenols derived from lignocellulosic wastes such as bark, sawdust, wood chips and the like.
The pyrolysis of lignocellulosic materials is known to produce a complex mixture of phenolic compounds which are derived primarily from the lignin contained in the feedstock. Such a complex mixture of phenolic compounds requires expensive fractionation in order to provide a phenolic fraction which can be used as a substitute for the petroleum-based phenol in the synthesis of phenolic resins. For example, in an attempt to formulate new adhesives for wood, Chum and Black have proposed in U.S. Pat. No. 4,962,269 a process for fractionating fast-pyrolysis oils derived from lignocellulosic materials to produce a phenolic compounds/neutrals fraction. The process involves a series of liquid-liquid extraction steps, wherein the phenolic compounds partitioned in an organic phase from the pyrolysis oil phase and the organic phase is then treated with an aqueous alkali metal bicarbonate solution. The complexity and lengthy solvent extraction associated with a relatively low yield of the phenolic compounds/neutrals fraction limit the industrial applications of such a process. The same disadvantages are encountered in the fractionation process described in U.S. Pat. No. 4,233,465.